The heating of rooms using a fireplace or fireplace furnace is well known in the prior art. Ordinarily, these prior art systems burn a fuel such as wood and are frequently very inefficient.
In an effort to improve the efficiency of fireplace furnaces and the like, prior art systems have provided for both a primary burning of the fuel and a secondary combustion of the flue gases. Prior U.S. Pat. Nos. which disclose secondary combustion include the following: 4,180,052 to Henderson, 4,078,541 to Roycraft; 4,111,181 to Canney; 1,341,580 to Pelton; and 4,192,285 to Nietupski. It has also been suggested in the prior art that an increase in the efficiency of fireplace furnaces can be achieved by directing the room air to be heated in a counter flow direction with respect to the flue gases produced by combustion of the fuel. Such a counter flow of the room air is disclosed in U.S. Pat. Nos. 4,089,320 to Brown et al and 3,171,399 to Kirgan.
While many of the prior art systems have significantly increased the efficiency of a fireplace furnace relative to an open fireplace, some of the heat produced by the burning of the fuel is still wasted. With the rising cost of fuel, the utilization of as much of the heat produced by the burning of the fuel is important.